Heat pumps have long been known and employed in the heating, ventilating, and air conditioning industry. A significant reason for the extensive use and focus of attention on heat pump systems is that the same components may be employed to effect both heating and cooling operations, whereas most other systems require a substantial number of separate equipment components for carrying out heating and cooling functions. Classically, heat pump systems employ a compressor which is operated by an electric motor to circulate refrigerant through a condenser which converts a gaseous form of the refrigerant to a liquid and an evaporator which absorbs heat from or imparts heat to an area to be cooled or heated, respectively.
For the most part, advancements in heat pump system technology have been directed to the development of improved working fluids and system components. In the case of working fluids, different refrigerants and particularly different fluorocarbon compounds have been developed which exhibit optimum performance characteristics in particular equipment or operating ranges. In regard to system components, efforts have been made to improve the operation and efficiency of the compressor, condenser, evaporator, and other ancillary components of these systems. However, due to the relatively advanced age and state of development of this technology, only minor improvements in operation and efficiency have been achieved through research and development efforts of this nature in recent years.
Attempts have been made to develop heat pumps which are heat driven. In this respect, engine driven and absorption type heat pumps represent examples of efforts of this type. Heat driven heat pumps of these types have not achieved commercial acceptance and recognition for a number of reasons. In general, devices of this nature tend to be highly complex systems having component elements which are both sophisticated and expensive. In addition, many of these systems contemplate the use of working fluids which are other than conventional refrigerants, such as ammonia or lithium bromide. Due to the fact that ammonia, for example, is considered to be a noxious gas, the use of nonconventional working fluids of this nature requires radically new and different capabilities and equipment with respect to installation, repair and service personnel that is not normally involved in the heating, ventilating, and air conditioning industry. With the technical limitations on working fluid and component improvements and the lack of commercial acceptance of heat driven heat pump systems, these systems have remained in essentially the same state of technological development for a substantial number of years.
Heat driven heat pumps employing heat engines and conventional working fluids have been developed but typically suffer from a number of disadvantages. For example, at the end of each power stroke of a heat engine piston, fluid at a high temperature of perhaps 300° F. and a high pressure of perhaps 160 p.s.i. remains in the heat engine cylinder. When this fluid is discharged into a condenser there is a loss of a significant amount of kinetic and thermal energy, thereby rendering the overall system highly inefficient.
Another problem area in such heat driven heat pumps is that it is desirable to combine the heat engine and compressor within a single housing having a piston rod connecting the heat engine piston and the compressor piston. Since the optimum characteristics for the working fluids in the heat engine and the compressor are substantially different, it is necessary to employ two different refrigerants. Under these circumstances, it is a common problem to have the higher pressure working fluid eventually migrate through any seals into the lower pressure working fluid and thereby adversely alter the operating characteristics of the lower pressure working fluid.
A further difficulty in the design of heat engines is in providing a valve to effect shifting between high vapor pressure power stroke and exhaust stroke. When a conventional valve shifts, it allows vapor to blast into the cylinder so rapidly that it induces the entire heat pump to vibrate or shake violently, thereby shortening the life of the heat engine and being otherwise objectionable. Efforts to slow the valve shift motion have been unsuccessful because vapor will leak by the valve when it slowly passes from high vapor pressure position to the exhaust position.
Another notorious problem with heat engines is in effecting start-up if the unit has not been running and is cold. When the power section heat generator or evaporator first begins to deliver hot vapor to the power chamber of the heat engine, it condenses before it can drive the piston. Since there is a limited amount of working fluid in the heat generator it can run low on working fluid before the power chamber of the heat engine reaches operating temperature. This causes overheating of the heat generator and possible scorching of the working fluid, thereby requiring major servicing before the heat pump can resume normal operation.
As a result of various of the above factors or combinations thereof, heat driven heat pump systems have not achieved any extent of commercial acceptance.